1. Field of the Invention
The present invention is directed generally toward integrated circuit technology. More specifically, the present invention is a power supply filter built into the chip carrier module of an integrated circuit.
2. Background of the Invention
Power supply noise is a fact of life in high-speed integrated circuit design. Particularly susceptible to such noise are high-frequency switching circuits, where load-induced switching noise may enter the power supply rails of the circuit, causing such problems as ground bounce.
Phase-locked loops (PLLs), in particular, are quite sensitive to this noise. For this reason, sensitive subcircuits such as a PLL often have their own dedicated power supply terminals that are separate from the power supply terminals of the other components. But although a PLL can be manufactured in an integrated circuit with dedicated power supply rails, it is not easily deployed in practice, since external filtering networks must be carefully designed to allow power supply noise from interfering with the operation of the PLL. This filter network design process is difficult and time-consuming. Thus ideally, an application-level developer would prefer not to have to design power supply filter networks to use with PLLs or other integrated circuits. It would be preferable, then, for the filter circuitry to be somehow incorporated into the integrated circuit package itself, so that an application-level developer need not be concerned with the design of the filter; it would simply be prefabricated for immediate use.
Ideally, this filter would be located on the integrated circuit itself to reduce the effects of parasitic inductance""s and resistance""s of connecting wires. This is not a practical solution, however, since at high frequencies, inductors are needed within the filter networks, and inductors are impractical to fabricate or simulate (e.g., with so-called xe2x80x9cgyratorxe2x80x9d circuits) in a silicon chip. Also, it should be noted that at low frequencies, although inductors are not necessary, relatively large capacitors are necessary, and these capacitors are not particularly practical to implement in an integrated circuit, either. Capacitors, in general, tend to take up a disproportionately large amount of space on an integrated circuit. Including a large number of capacitors on a integrated circuit may also cause leakage currents to be generated, which is also undesirable.
Thus, what is needed is an integrated circuit, and in particular a PLL integrated circuit, that eliminates the need for external power supply filtering in an application circuit.
The present invention provides a power-supply filter that is built into an integrated circuit package. An LC, RC, or RLC filter is built into the integrated circuit""s chip carrier module and connected so as to filter the power supply entering the integrated circuit. By manufacturing the filter as part of the integrated circuit package, a chip manufacturer can eliminate the need for application-level developers to provide an external filtering network in the deployment of the integrated circuit in an application circuit.